This invention relates to a resist material used for production of a semiconductor device, etc. Particularly, the present invention relates to a resist material for forming a positive pattern using deep ultraviolet (DUV) light having a wavelength of 300 nm or less, such as KrF excimer laser beams having a wavelength of 248.4 nm, etc.
In recent years, the wavelength of light from the light source of an exposing apparatus used for micro-fabrication, in particular, photolithography has been shortened with an enhancement of the degree of integration of semiconductor devices. Currently, employment of KrF excimer laser beams (248.4 nm) is being investigated. However, a resist material suitable for this wavelength has not yet been found.
For example, as resist materials used in the case of using a light source capable of emitting KrF excimer laser beams or deep ultraviolet light, there have been developed dissolution-inhibiting type resist materials comprising a resin having high transmittance for light of near 248.4 nm and a photosensitive compound having a diazodiketo group in the molecule (for example, Japanese Patent Unexamined Publication Nos. 1-80944, 1-154048, 1-155338, 1-155339 and 1-188852, and Y. Tani et al., SPIE's 1989 Sympo., 1086-03, etc.). However, these dissolution-inhibiting type resist materials, in common with one another, have a low sensitivity and hence cannot be used in the case of employment of deep ultraviolet light or KrF excimer laser beams which requires a highly sensitive resist material. On the other hand, for reduction of the amount of exposure energy (enhancement of the sensitivity), there has been proposed recently a chemical amplified type resist material in which an acid generated by exposure to light is used as a catalyst [H. Ito et al., Polym. Eng. Sci., 23, 1012 (1983)]. On such chemical amplified type resist materials, various reports have been presented [for example, H. Ito et al., U.S. Pat. No. 4,491,628 (1985); J. V. Crivello, U.S. Pat. No. 4,603,101 (1986); W. R. Brunsvolt et al., SPIE's 1989 Sympo., 1086-40; T. Neeman et al., SPIE's 1989 Sympo., 1086-01; and Japanese Patent Unexamined Publication No. 62-115440). Such chemical amplified type resist materials, however, involve the following problems. When there is used in them a phenol ether type resin such as poly(4-tert-butoxycarbonyloxystyrene), poly(4-tert-butoxycarbonyloxy-.alpha.-methylstyrene), poly(4-tert-butoxystyrene), poly(4-tert-butoxy-.alpha.-methylstyrene) or the like, all of the chemical amplified type resist materials have poor heat resistance and are disadvantageous in that because of their low adhesive properties to a substrate, film peeling tends to occur during development, so that no satisfactory pattern can be obtained. When there is used a carboxylic acid type resin such as poly(tert-butyl-4-vinylbenzoate) or the like, the chemical amplified type resist materials are insufficient in light-transmitting properties near 248.4 nm because of the aromatic ring. When there is used a poly(tert-butylmethacrylate) or the like, the heat resistance and dry etching resistance of this resin are poor. A resist material using a silyl group-containing polymer is also disclosed (e.g. Japanese Patent Examined Publication No. 3-44290, etc.). When p-trimethylsilyloxystyrene polymer or p-tert-butylidmethylsilyloxystyrene polymer is used, there arise problems in that the sensitivity is low, complete stripping off of the resist by ashing according to an oxidizing plasma process is impossible due to containing silicon, etc. Thus, practical application was almost impossible.
As resist materials free from the above defects, there have recently been reported a resist material obtained by use of a copolymer of p-tertbutoxycarbonyloxystyrene and p-hydroxystyrene (Japanese Patent Unexamined Publication No. 2-209977), resist materials obtained by use of a copolymer of p-tetrahydropyronyloxystyrene and p-hydroxystyrene (Japanese Patent Unexamined Publication Nos. 2-19847, 2-161436 and 2-25850), a resist material obtained by use of a copolymer of p-tert-butoxystyrene and p-hydroxystyrene (Japanese Patent Unexamined Publication No. 2-62544), etc. However, when these copolymers such as p-tert-butoxycarbonyloxystyrene/p-hydroxystyrene, p-tetrahydropyranyloxystyrene/p-hydroxystyrene, p-tert-butoxystyrene/p-hydroxystyrene, etc. are used as the resin component, it is necessary to make a strong acid present as a catalyst in order to maintain high sensitivity and to release protective groups such as a tert-butoxycarbonyl group, a tetrapyranyl group, a tert-butyl group, etc. for obtaining alkali solubility. In order to attain such a purpose, there is used a photosensitive compound which generates a remarkably strong acid by exposure to light, e.g. a triphenylphosphonium salt, a diphenyliodonium salt, tris(trichloromethyl)-s-triazine/triethanolamine, or the like, in a resist material containing the above-mentioned copolymer as the resin component. When a pattern formation is carried out in the presence of such a strong acid, there often takes place a remarkable dimensional change of pattern with a time delay between exposure and post exposure bake (PEB), and sometimes no pattern is formed. Thus, even if a pattern can be formed in a remarkably short time, a good pattern formation cannot be expected in a practical production wherein a considerable time is required from the light exposure to heating treatment.
Further, the above-mentioned photosensitive compounds are generally unstable, so that resist materials containing them are also poor in storage stability. In any way, there is a problem in that these cannot be used as they are.
A further problem of the above-mentioned polymers or copolymers is in that the group used as a protective group for the hydroxyl group (e.g. a tert-butoxycarbonyl group, a tert-butyl group, a trimethylsilyl group, a tetrahydropyranyl group, etc.) is not completely released even in the presence of a strong acid. Thus, a polymer or copolymer containing a monomer component having a hydroxyl group protected with such a protective group is used as a resin component in a resist material, the difference in dissolution rate for an alkali developer between light exposed portions and nonexposed portions of the resist material is small, resulting in making insufficient resolution ability.
Although thus the chemical amplified type resist materials have a higher sensitivity than do conventional resist materials, they involve problems of, for example, poor in heat resistance of resin, poor adhesive properties to a substrate, insufficient transmittance for light of near 248.4 nm, insufficient resolution, and change of the dimensions of a pattern with a time delay between exposure and post exposure bake (PEB). Therefore, they are difficult to put to practical use. Accordingly, there is eagerly desired a practical highly sensitive resist material free from all of the above problems.